As optical information readers, bar code readers that read bar codes indicating information such as names, prices, and so on of products are in wide use in the distribution industry and the retail industry.
These bar code readers are broadly classified into a hand type and a fixed type, and further the hand type includes a pen type, a touch type, and a light beam scanning type (laser type). The fixed type is a light beam scanning type designed to be capable of scanning in a plurality of directions.
Among these readers, an optical information reader that is a target of the invention is one corresponding to the hand type bar code reader by the light beam scanning type.
The bar code reader of the light beam scanning type brings laser light generated by a light source such as laser diode (semiconductor laser) or the like into beam form, deflects the light beam by a reflecting mirror to cause it to impinge on a bar code, rotates or vibrates (oscillates) the reflecting mirror to scan the bar code in such a manner that the light beam traverses the bar code.
Then, reflected light from the bar code is condensed and received by a receiving sensor to be converted into an electric signal. The electric signal is subjected to A/D conversion and encoded, and outputted as bar code read information.
Typical light beam scanning mechanisms used in such a conventional optical information reader of the light beam scanning type are one using a polygon mirror and a rotary drive motor and one using a single face mirror and a galvano motor.
Each of these light beam scanning mechanisms, however, is difficult to be reduced in dimensions in its height direction (direction of a rotation shaft) and a direction orthogonal thereto because the polygon mirror and the rotary drive motor or the single face mirror and the galvano motor are separated bodies which are coupled to each other by a rotation shaft directly or via a reduction mechanism.
Hence, to solve such a disadvantage of the conventional light beam scanning mechanism, the present inventor et al. provided vibration mirror type scanner that is reduced in size by integrating a reflecting mirror, a movable magnet, and a rotation shaft (see JP H7-261109 and JP H8-129600).
Whereas, in the market thereafter, for further enhancement of convenience of such an optical information reader, further expansion of uses, and creation of new type of usage, it is demanded to further reduce in size, thickness, and weight a vibration mirror scanning part forming a core part of the reader. Therefore, the present inventor et al. further develop and provide for the market a vibration mirror type scanner intended to achieve the aforementioned reduction in size, thickness, and weight and coping with the need for further improvement in scanning frequency and a maximum scanning angle of a light beam and the need for correction control of scanning characteristics and temperature characteristics of the beam (see JP H11-213086).
Further, as a technique on the reduction in size, thickness, and weight of the optical information reader that is the demand of the market, there provided is a one-piece optical assembly for an optical scanner (see JP H11-326805), a retroreflection scanning module for an electro-optic reader (see JP 2000-298242), or the like as one in which a laser diode, a light detector, various optical elements, and so on are positioned and accommodated in a molded resin member for assembly or modularization.
On the other hand, in the optical information reader of the light beam canning type, it is necessary that a light emitting unit with a laser diode as a light source, a collimator lens for bringing laser light emitted by the laser diode into a parallel luminous flux, and a member provided with an aperture for emitting the resulting laser light in a thin beam are positioned and secured in a lens-barrel with their optical axes coinciding one another.
Collimator lenses are not uniform in size (for example, diameter) and have some error, and therefore it is necessary to give slight room to the inner diameter of the lens-barrel so that all of the collimator lenses can be fitted thereinto. Further, there is a small but real error in the positional accuracy of the laser diode in the light emitting unit. To correct these errors, means for correcting the optical axis is required.
Therefore, for example, a structure shown in FIG. 31 has been employed as the structure of a conventional laser beam generating part. Specifically, a flange for optical axis adjustment 103 is adhered to a light emitting unit 102, a light emitting part 102a of the light emitting unit 102 is inserted into a lens-barrel 101 provided in a casing whose illustration is omitted from one end face side thereof, and the flange for optical axis adjustment 103 is secured to the lens-barrel 101 with screws 104. Further, an O-ring 105 and a collimator lens 106 are inserted into the lens-barrel 101 from the other end face side, and an aperture ring 107 with an aperture 108 formed at the center is screwed into the lens-barrel 101 so that the collimator lens 106 is sandwiched and secured between the aperture ring 107 and a flange part 101a in the lens-barrel 101 with the O-ring 105 giving preload thereto.
In this event, the screw-in amount of the aperture ring 107 is adjusted so that a light emitting point of the light emitting unit 102 is at a position slightly farther than a focus point of the collimator lens 106. Further, the attachment position in the diameter direction of the light emitting unit 102 by the flange for optical axis adjustment 103 and the screws 104 is adjusted so that the optical axes of the collimator lens 106 and light emitting unit 102 coincide with each other. For that purpose, the inner diameter of a screw insertion hole 103a of the flange for optical axis adjustment 103 is made larger than the outer diameter of the screw 104, thereby enabling fine adjustment of the attachment position in the diameter direction of the light emitting unit 102.
However, since the demanded accuracy of attachment of the light emitting unit and collimator lens in the laser beam generating part is very high, it is difficult to achieve the demanded accuracy of optical axis adjustment and focus adjustment in this kind of conventional attachment structure. In addition, as shown in FIG. 31, the flange for optical axis adjustment 103 for adjusting the optical axis of a laser is adhered to the rear part of the light emitting unit 102 and both are screwed to the end face of the lens-barrel 101, and therefore the number of components necessarily increases and screwed parts occupy a large capacity, leading to an obstacle to a reduction in size and price.
Hence, there also is a reader in which the optical axis adjustment mechanism is omitted to reduce the size and the number of components of the laser beam generating part. This, however, increases variations in the optical axis, resulting in variations of about ±4° in the scan direction.
Besides, enhanced reading accuracy of the bar code symbol might cause wrong information to be also read. There can be as well printing nonuniformity of the bar code symbol and ink scattered to spaces in the bar code symbol as blurred black bars and so on. Further, optical noise is also caused by a speckle pattern (grain-like flicker occurring when a laser beam is applied) generated by a laser beam on bar code paper surface. There is a problem that even though the above-described defects are small enough not be recognized by the naked eye, a reader with enhanced reading accuracy may catch them as signals.
It is difficult to avoid such optical noise in the optical information reader of the scanning type by a laser beam, but it is desirable to decrease its influence as much as possible.
Besides, in a module for an optical information reader in recent years, an LSI (large-scale integration circuit) is used to process an electric signal made from reflected light from a bar code detected by a light receiving sensor or to control respective parts in the module.
Typically, this LSI is mounted on a circuit board that is to be attached to the top or the side of the main body of the module.
However, depending on the use environment of the optical information reader, various kinds of electronic devices are often used, and there is a serious problem that the above-described LSI is affected by the electromagnetic wave noise caused by these devices. In addition, since mobile phones have become widespread and are used not only for a simple telephone function but also as information terminals, existence of a plurality of mobile phones in a work area is not uncommon, and therefore it is also necessary to consider the influence of electromagnetic wave noise caused by those phones.
Hence, to avoid those noises, the LSI mounted on the top or the side of the module main body is covered with a metal plate for shield in the prior art.
However, the module becomes bulky by the volume of the metal plate in addition to the thickness of the LSI, leading to one of the obstacles to a reduction in size. In addition, the need for the metal plate increases the number of components as well as the number of attachment steps thereof.
It is an object of the invention to modularize the primary part of an optical information reader of the light beam scanning type, simplify the structures of attachment parts of a light emitting unit and a collimator lens, and enable read with highly accuracy, so as to reduce the size and price of the optical information reader. It is another object to eliminate most of the variation with time and the influence of the above-described optical noise and electromagnetic wave noise, so as to enable information read with high accuracy for a long time.